1. Field of the Invention
The present invention relates to a method of inspecting semiconductor elements or semiconductor devices formed on a wafer, and more particularly to an inspection apparatus for measuring electrical characteristics during semiconductor manufacture processes such as probing inspection and burn-in inspection.
2. Description of the Related Art
Manufacture processes for semiconductor elements such as ICs (Integrated Circuits) and LSIs (Large Scale Integrated circuits) are roughly classified into pre-processes until circuits are formed on a silicon wafer surface and post-processes until the silicon wafer is scribed into separate chips which are sealed by resin, ceramic or the like. At a predetermined stage during the pre-process, the electrical characteristics of each circuit of a semiconductor device is inspected to judge whether each chip is good or defective. The electrical characteristic inspection is divided into probing inspection for judging conduction error between circuits and burn-in inspection for selecting defective circuits at an accelerated speed by applying thermal and electrical stress to the circuit at a high temperature of about 150xc2x0 C.
Both the probing inspection and burn-in inspection use generally similar connection means for the connection between a test wafer and an external inspection system. More specifically, conductive fine probes are mechanically pushed against electrode pads made of aluminum alloy or another alloy patterned on a test wafer at a pitch of several tens xcexcm to several hundreds xcexcm and having a square shape of several tens to several hundreds xcexcm and about 1 xcexcmm thick.
The structure of a conventional probe is shown in FIGS. 13 and 14.
In the example shown in FIG. 13, each probe 141 is generally made of tungsten and having a fine needle with its tip diameter of several tens xcexcm and a length of several tens mm. The probe 141 is fixed to a substrate 142 or insulating jig 143 or deformed in order that its tip is aligned to a corresponding electrode pad on a test wafer.
In the example shown in FIG. 14, each probe 151 is a metal projection formed on the surface of an organic thin film 152 such as a polyimide film. The metal projection is a semisphere metal projection formed mainly by a repetition of a plating process or a conical metal projection formed by using an anisotropically etched hole in a silicon substrate as the plating mold. A set of such projections are formed on the surface of the organic thin film 152.
Means for solving the problems of these two conventional techniques to be described later is made public in the publications JP-A-6-123746, JP-A-7-7052, JP-A-8-50146, and JP-A-9-243663.
In the publication JP-A-6-123746, notches are formed in an elastically deformable card and a plurality of elastically deformable probe needles are uniformly formed. The tip of each probe needle is formed with a plurality of contact members capable of contacting an electrode of a semiconductor element.
In the publication JP-A-7-7052, an electrical characteristic measuring probe has a cantilever structure made of at least one of a single crystal silicon layer, a silicon oxide layer, a silicon nitride layer, a polysilicon layer and a metal layer. The surface of the cantilever structure is coated with a conductive metal film and held by an insulating substrate with a conductive wiring pattern, to thereby use it as the probe.
In the publication JP-9-243663, a silicon substrate worked to have a diaphragm is formed with a plurality of contact probes on the contact surface of the diaphragm. Elastomer is coated on the diaphragm to form an electrical characteristic measuring probe.
The conventional method of inspecting a semiconductor device as described above has the following problems.
With the probe structure shown in FIG. 13, it takes a long time to align and fix each probe with a high precision, and mass production of inexpensive probe structures is difficult. In addition, a number of regions for aligning and fixing respective probes are necessary. It is therefore difficult to dispose a number of probes on a substrate, and the number of electrode pads or chips capable of being inspected collectively at one time is limited. Further, since the length of each probe is as long as about several tens mm, the parasitic capacitance of each probe is large so that it is practically impossible to inspect a high speed device of about 100 Mhz.
Still further, the radius of curvature of each probe tip is large. In order to break the insulating natural oxide film formed on the surface of an electrode pad of a test wafer, it is necessary to apply a large pressure load and scribe the electrode pad surface. Therefore, the probe tip is fast to be abraded, the life time (durable inspection times) of the probe is short, and electrode pad dusts generated during scribing may contaminate the semiconductor device manufacture environment.
With the probe structure shown in FIG. 14, probes are disposed at a fine pitch on the surface of the organic thin film such as polyimide, in correspondence with the positions of electrode pads of a test wafer. If there is a variation in warp of test wafers or in height of probes, it is difficult to absorb each distance variation between the probe and a corresponding electrode pad. The probe uses as its base member the organic thin film such as a polyimide film whose coefficient of linear expansion is greatly different from that of a test wafer. Therefore, in the burn-in inspection at a high temperature of about 150xc2x0 C., there is a large difference of linear expansion coefficient between the probe and test wafer, so that position misalignment may exist between the probe and the electrode pad positioned remotely from the center of the test wafer.
According to the publication of JP-A-6-123746, the card is made of synthetic resin or metal. It is therefore difficult to align probes at a fine pitch corresponding to the positions of electrode pads of a test wafer, i.e., difficult to form a plurality of probe needles each being elastically deformable.
In the publication of JP-A-7-7052, each cantilever probe made of a silicon based member is bonded to the surface of another insulating substrate. Therefore, a manufacture yield is low and the height of respective probes is irregular.
In the publication of JP-A-9-243663, it is described that the diaphragm formed on the silicon substrate deforms in conformity with deformation of a test wafer, because of use of elastomer (elastic material). However, this approach does not consider a variation in thicknesses of diaphragms. If a diaphragm having a variation in warp or thickness is deformed, the height of the contact probe cannot be controlled. Since the depth direction of the electrical characteristic measuring pad of a test wafer cannot be controlled, some area of the pad does not contact the probe if a pressure force is insufficient. Conversely, if the pressure force is too large, the probe may move deep under the pad and the test wafer may be broken.
In each of the probe structures described above, electrical wiring leads between the tips of probes and an external inspection system are formed on the same surface as the probe forming surface of the substrate. It is therefore necessary to form all external contact terminals to be concentrated on the outer peripheral area of the substrate. The area capable of forming external contact terminals is therefore limited, and it is difficult to electrically connect a number of probes to the external. It is difficult to perform a broad area simultaneous inspection, such as inspection of all electrode pads of a test wafer collectively at one time.
It is an object of the present invention to solve many problems described above and provide an apparatus and method of inspecting the electrical characteristics of a semiconductor device, capable of inspecting collectively at one time all electrode pads in a large area of, for example, a test wafer, to thereby improve manufacture yield, lower manufacture cost and provide a semiconductor apparatus which is inexpensive and highly reliable.
In order to achieve the above object, in a method of inspecting a semiconductor element by directly contacting the element to an inspection apparatus according to an aspect of the present invention, a beam structure or a diaphragm structure is formed on a substrate with probes, the structure being capable of deforming the probes by a pressure force, and a mechanism for pressing or fixing a test wafer with electrode pads of test semiconductor elements or a mechanism for pressing the probes on the substrate or the probe peripheral areas, is provided. The substrate with the probes is made of silicon, and the probe is made of silicon, metal or a compound thereof, and a wiring lead of conductive material extends to the back surface of the probe forming substrate by using an intermediate insulating member. A flat portion is formed at the tip portion of the probe so that the probe height can be made constant with a high precision.
It is preferable to from a probe on an independent both-end supported beam. The structure may be used in which a beam of a swastika-shape is formed around the probes disposed in an central area of a chip. The structure including the beam is formed by anisotropic etching or dry etching. For the dry etching, an inductively coupled plasma-reactive ion etching (ICP-RIE) system is used so that the space between beams can be narrowed and the narrow pitch between devices can be dealt with.
The wiring lead is passed through an inspection wafer via a through hole formed by anisotropic etching or dry etching, and the probe forming surface of the substrate and the back surface thereof are electrically wired by utilizing sputtering, vapor deposition, or plating. The through hole of the inspection wafer is preferably formed by dry etching. Very inexpensive semiconductor elements or electronic components can be provided by using the above-described inspection structure and method.